2008 YZ450 Hard Starting


8 replies to this topic
  • WGP

Posted February 20, 2012 - 12:33 PM

#1

2008 YZ450

Bike is hard to start when it has been shut off for 10 minutes or more. Strange problem.

I have searched on hard starting and nothing really helped.

Bike is at 4500 elevation and the temps run from 20-80F (high desert) JD red #4 168m 45p FMF exhaust, 2.5 out on f screw

It runs like a champ, no bogging, hesitation ect... Valves are all in spec.

When the bike is cold and its cold out like below 40F is will usually start on the 5-6 kick using 2 twists of throttle, choke out and kick w/ no throttle. Sometimes it will flood a little bit and will have to pull in hotstart and it will fire.

When the motor is warm and I have been riding, I can shut it off and it will fire right back up using hotstart.

BUT if the bike sits for 10 minutes or more, it doesn't want to start! Driving me nuts!

The biggest problem is racing because of dead engine starts. I'm getting killed!

It will start but I have to kick it like 10 -20 times. My guess is that its got to much gas?

Searching the forum someone said that adjustments for starting the bike are only in:

Float bowl height
Starter Jet
Idle speed (rpms)

Starter jet is stock, Idle may be a little low but not much, I have never checked float height.
The Carb is cleaned out every 6 months

Any thoughts?

  • yz450fcranker

Posted February 20, 2012 - 02:35 PM

#2

i had a bad crankshaft in my 2009 replaced at the dealership now runs like a champ again

  • Gunner354

Posted February 20, 2012 - 03:00 PM

#3

Might be a float issue.

  • grayracer513

Posted February 20, 2012 - 03:05 PM

#4

It will start but I have to kick it like 10 -20 times. My guess is that its got to much gas?

Searching the forum someone said that adjustments for starting the bike are only in:

Float bowl height
Starter Jet
Idle speed (rpms)



If I had to guess, I'd be more inclined to say too little gas. It's not exactly warm in Nevada these days, is it? It looks like it's been hard to get into the 70's. Bike could be cooling off more quickly that you think. Try a single half twist of throttle or maybe one kick with the choke on. Works on mine.
  • Float level influences everything, and just has to be right, within a half mm if possible.
  • Starter jet works only when the choke is used. It's how fuel gets into that circuit.
I would have suggested dirt in the float bowl (and don't rule that out, either) but you said the carb gets cleaned frequently. Idle speed does have an effect, but the pilot (idle) circuit mixture, both the jet and the adjustment screw is very important. Look in the Common Threads Sticky under Carburetor for a bunch of useful info. Keep it slightly on the lean side and you'll stall less and start easier. Mine starts so easy sometimes it's actually funny watch.

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  • WGP

Posted February 20, 2012 - 03:15 PM

#5

Thanks I'll check the float level and report back...
I assume its in the YZ book for proper height, never touched it, any tips would be great.

L8R

  • Gunner354

Posted February 20, 2012 - 06:48 PM

#6

Not a fan of aftermarket jet kits so it's hard to tell with you using one.
The idle plays a huge role in starting .Try turning it way up and see if it starts easier.
I have two 09 yzs and a few friends with the same. We run 48 pilot, stock needle in stock 3rd position and two of us run a 162 main and two others a 168 main. Fuel screw at 1 1/2. Our bikes run from sea level to 7K ft. 20* to 90 plus with no change in jetting. Starts are normally 1-2 kicks. When cold I do two quick throttle twists to add a little extra fuel.

Edited by Gunner354, February 20, 2012 - 06:49 PM.


  • WGP

Posted March 25, 2012 - 08:42 AM

#7

So I checked the float level and it was right on.....

The idle was a little too low so I set it higher and I turned the fuel screw in a turn. It starts the way it should now. (Almost!)

It seems I need to crack the throttle 1/8" and Kick to start it.

What does that mean?

  • Gunner354

Posted March 25, 2012 - 10:53 AM

#8

So I checked the float level and it was right on.....

The idle was a little too low so I set it higher and I turned the fuel screw in a turn. It starts the way it should now. (Almost!)

It seems I need to crack the throttle 1/8" and Kick to start it.

What does that mean?


Probably still to rich. Try turning the fuel screw in a little more and see if it's better or worse.
The jet kit usually runs on the rich side to be safe.
I would ditch the jet kit and run my jetting!

  • WGP

Posted March 25, 2012 - 05:44 PM

#9

The JD needle is old and is worn 3/4 the way down, looks scratched? Wonder if this affects things?

I'm basically running the same jetting though except my pilot is leaner because I never ride below 4000'





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